Use named arrays to store streams for stream_select().
Use named arrays to store streams for stream_select().

This makes detecting existing stream entries faster, and stream_select()
does not seem to care about arrays with non-sequential keys.

steverhoades/event-loop,kaduev13/event-loop,mkrauser/event-loop,kaduev13/event-loop,reactphp/event-loop,mkrauser/event-loop,clue-labs/event-loop,steverhoades/event-loop